WASHINGTON  Pollution experts have "serious scientific concerns" that newly unveiled U.S. air quality standards may pose risks to human health and welfare, according to a letter made public Tuesday.

The experts, all charter members of a key advisory panel to the U.S. Environmental Protection Agency, questioned the agency's decision to keep annual standards for fine soot particles at the same level they have been since 1997.

The panel's scientists, along with a broad range of environmental and health groups, had sought to lower the amount of soot permissible, citing research that showed health risks from even small amounts over the course of a year.

"There is clear and convincing evidence that significant adverse human-health effects occur in response to short-term and chronic particulate matter exposures at or below 15 micrograms per cubic meter (of air), the level of the current annual ... standard," the experts wrote in a Sept. 29 letter to EPA Administrator Stephen Johnson.

Johnson announced the decision to leave this standard unchanged on Sept. 21, saying it offered "cleaner air to all Americans," and would reduce premature deaths, heart attacks and hospital stays for people with heart and lung disease and bring health benefits valued at between $20 billion and $160 billion a year.

INDUSTRY'S VIEWPOINT

While Johnson agreed with the advisory panel to strengthen daily air quality standards by nearly 50 percent, he did not follow their recommendation to reduce the annual standard to 13 or 14 micrograms per cubic meter of air.

Rogene Henderson of the Lovelace Respiratory Research Institute, who chairs EPA's Clean Air Scientific Advisory Committee and who signed the letter along with six other panel members, said the key concern was for health and welfare.

"The main thing is to protect the public health," Henderson said in a telephone interview from Albuquerque, New Mexico. The unchanged annual standards do not provide a margin of safety, as stipulated by the U.S. Clean Air Act.

EPA spokeswoman Jennifer Wood, in an e-mail response to questions about the scientists' letter, said, "Where the science was clear, EPA took clear action."

"Administrator Johnson fully considered the science, (the panel's) advice about the science and more than 120,000 public comments in making his policy decisions about the appropriate levels of the particle pollution standards," Wood said.

However, Henderson and others have noted that 20 of the 22 members of the full advisory committee advised more stringent annual standards. The two who advised against tightening the standards were a former longtime employee of General Motors and the former president of the Chemical Industry Institute of Toxicology, funded by chemical companies.

"I think they did present the industry viewpoint," Henderson said of these two members. "They would say they based it on science."